1. Field of the Invention
The present invention relates to an electrode for a fuel cell, and a membrane-electrode assembly and fuel cell system including the membrane-electrode assembly. More particularly, the present invention relates to an electrode for a fuel cell that can lower the cost of a fuel cell and implement a high power fuel cell, and a membrane-electrode assembly and fuel cell system including the membrane-electrode assembly.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and a fuel, such as hydrogen, or a hydrocarbon-based material such as methanol, ethanol, natural gas, and the like. The polymer electrolyte fuel cell is a clean energy source that is capable of replacing fossil fuels. It has advantages, such as high power output density and energy conversion efficiency, operability at room temperature, and being small-sized and tightly sealed. Therefore, it can be applicable to a wide array of fields, such as non-polluting automobiles, and electricity generation systems and portable power sources for mobile equipment, military equipment, and the like.
Representative exemplary fuel cells include Polymer Electrolyte Membrane Fuel Cells (PEMFCs) and Direct Oxidation Fuel Cells (DOFCs). The DOFC includes a direct methanol fuel cell that uses methanol as a fuel.
The PEMFC has an advantage of a high energy density and high power, but it also has problems in the need to carefully handle hydrogen gas and the requirement for accessory facilities, such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel gas.
On the contrary, a DOFC has a lower energy density than that of the polymer electrolyte fuel cell, but has the advantages of easy handling of the liquid-type fuel, a low operation temperature, and no need for additional fuel reforming processors.
In the above-mentioned fuel cell system, a stack that generates electricity includes several to scores of unit cells stacked adjacent to one another, and each unit cell is formed of a Membrane-Electrode Assembly (MEA) and a separator (also referred to as a bipolar plate). The MEA is composed of an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”) that are separated by a polymer electrolyte membrane.
A fuel is supplied to the anode and adsorbed on catalysts of the anode, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into the cathode via an external circuit, and the protons are transferred into the cathode through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode, and then the oxidant, protons, and electrons react on catalysts of the cathode to produce electricity along with water.